mir-canon: First commit.

mir-canon (MIRCanonicalizerPass) is a pass designed to reorder instructions and
rename operands so that two similar programs will diff more cleanly after being
run through mir-canon than they would otherwise. This project is still a work
in progress and there are ideas still being discussed for improving diff
quality.

M    include/llvm/InitializePasses.h
M    lib/CodeGen/CMakeLists.txt
M    lib/CodeGen/CodeGen.cpp
A    lib/CodeGen/MIRCanonicalizerPass.cpp


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317285 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/InitializePasses.h

@@ -377,6 +377,7 @@ void initializeWinEHPreparePass(PassRegistry&);
 void initializeWriteBitcodePassPass(PassRegistry&);
 void initializeWriteThinLTOBitcodePass(PassRegistry&);
 void initializeXRayInstrumentationPass(PassRegistry&);
+void initializeMIRCanonicalizerPass(PassRegistry &);
 
 } // end namespace llvm
 

lib/CodeGen/CMakeLists.txt

@@ -113,6 +113,7 @@ add_llvm_library(LLVMCodeGen
   RegisterPressure.cpp
   RegisterScavenging.cpp
   RenameIndependentSubregs.cpp
+  MIRCanonicalizerPass.cpp
   RegisterUsageInfo.cpp
   RegUsageInfoCollector.cpp
   RegUsageInfoPropagate.cpp

lib/CodeGen/CodeGen.cpp

@@ -99,6 +99,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeVirtRegRewriterPass(Registry);
   initializeWinEHPreparePass(Registry);
   initializeXRayInstrumentationPass(Registry);
+  initializeMIRCanonicalizerPass(Registry);
 }
 
 void LLVMInitializeCodeGen(LLVMPassRegistryRef R) {

lib/CodeGen/MIRCanonicalizerPass.cpp

@@ -0,0 +1,626 @@
+//===-------------- MIRCanonicalizer.cpp - MIR Canonicalizer --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The purpose of this pass is to employ a canonical code transformation so
+// that code compiled with slightly different IR passes can be diffed more
+// effectively than otherwise. This is done by renaming vregs in a given
+// LiveRange in a canonical way. This pass also does a pseudo-scheduling to
+// move defs closer to their use inorder to reduce diffs caused by slightly
+// different schedules.
+//
+// Basic Usage:
+//
+// llc -o - -run-pass mir-canonicalizer example.mir
+//
+// Reorders instructions canonically.
+// Renames virtual register operands canonically.
+// Strips certain MIR artifacts (optionally).
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetInstrInfo.h"
+
+#include <queue>
+
+using namespace llvm;
+
+namespace llvm {
+extern char &MIRCanonicalizerID;
+} // namespace llvm
+
+#define DEBUG_TYPE "mir-canonicalizer"
+
+static cl::opt<unsigned>
+CanonicalizeFunctionNumber("canon-nth-function", cl::Hidden, cl::init(~0u),
+                           cl::value_desc("N"),
+                           cl::desc("Function number to canonicalize."));
+
+static cl::opt<unsigned>
+CanonicalizeBasicBlockNumber("canon-nth-basicblock", cl::Hidden, cl::init(~0u),
+                             cl::value_desc("N"),
+                             cl::desc("BasicBlock number to canonicalize."));
+
+namespace {
+
+class MIRCanonicalizer : public MachineFunctionPass {
+public:
+  static char ID;
+  MIRCanonicalizer() : MachineFunctionPass(ID) {}
+
+  StringRef getPassName() const override {
+    return "Rename register operands in a canonical ordering.";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+
+} // end anonymous namespace
+
+enum VRType { RSE_Reg = 0, RSE_FrameIndex, RSE_NewCandidate };
+class TypedVReg {
+  VRType type;
+  unsigned reg;
+
+public:
+  TypedVReg(unsigned reg) : type(RSE_Reg), reg(reg) {}
+  TypedVReg(VRType type) : type(type), reg(~0U) {
+    assert(type != RSE_Reg && "Expected a non-register type.");
+  }
+
+  bool isReg()        const { return type == RSE_Reg;          }
+  bool isFrameIndex() const { return type == RSE_FrameIndex;   }
+  bool isCandidate()  const { return type == RSE_NewCandidate; }
+
+  VRType getType() const { return type; }
+  unsigned getReg() const {
+    assert(this->isReg() && "Expected a virtual or physical register.");
+    return reg;
+  }
+};
+
+char MIRCanonicalizer::ID;
+
+char &llvm::MIRCanonicalizerID = MIRCanonicalizer::ID;
+
+INITIALIZE_PASS_BEGIN(MIRCanonicalizer, "mir-canonicalizer",
+                      "Rename Register Operands Canonically", false, false);
+
+INITIALIZE_PASS_END(MIRCanonicalizer, "mir-canonicalizer",
+                    "Rename Register Operands Canonically", false, false);
+
+static std::vector<MachineBasicBlock *> GetRPOList(MachineFunction &MF) {
+  ReversePostOrderTraversal<MachineBasicBlock *> RPOT(&*MF.begin());
+  std::vector<MachineBasicBlock *> RPOList;
+  for (auto MBB : RPOT) {
+    RPOList.push_back(MBB);
+  }
+
+  return RPOList;
+}
+
+// Set a dummy vreg. We use this vregs register class to generate throw-away
+// vregs that are used to skip vreg numbers so that vreg numbers line up.
+static unsigned GetDummyVReg(const MachineFunction &MF) {
+  for (auto &MBB : MF) {
+    for (auto &MI : MBB) {
+      for (auto &MO : MI.operands()) {
+        if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+          continue;
+        return MO.getReg();
+      }
+    }
+  }
+
+  return ~0U;
+}
+
+static bool rescheduleCanonically(MachineBasicBlock *MBB) {
+
+  bool Changed = false;
+
+  // Calculates the distance of MI from the begining of its parent BB.
+  auto getInstrIdx = [](const MachineInstr &MI) {
+    unsigned i = 0;
+    for (auto &CurMI : *MI.getParent()) {
+      if (&CurMI == &MI)
+        return i;
+      i++;
+    }
+    return ~0U;
+  };
+
+  // Pre-Populate vector of instructions to reschedule so that we don't
+  // clobber the iterator.
+  std::vector<MachineInstr *> Instructions;
+  for (auto &MI : *MBB) {
+    Instructions.push_back(&MI);
+  }
+
+  for (auto *II : Instructions) {
+    if (II->getNumOperands() == 0)
+      continue;
+
+    MachineOperand &MO = II->getOperand(0);
+    if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+      continue;
+
+    DEBUG(dbgs() << "Operand " << 0 << " of "; II->dump(); MO.dump(););
+
+    MachineInstr *Def = II;
+    unsigned Distance = ~0U;
+    MachineInstr *UseToBringDefCloserTo = nullptr;
+    MachineRegisterInfo *MRI = &MBB->getParent()->getRegInfo();
+    for (auto &UO : MRI->use_nodbg_operands(MO.getReg())) {
+      MachineInstr *UseInst = UO.getParent();
+
+      const unsigned DefLoc = getInstrIdx(*Def);
+      const unsigned UseLoc = getInstrIdx(*UseInst);
+      const unsigned Delta = (UseLoc - DefLoc);
+
+      if (UseInst->getParent() != Def->getParent())
+        continue;
+      if (DefLoc >= UseLoc)
+        continue;
+
+      if (Delta < Distance) {
+        Distance = Delta;
+        UseToBringDefCloserTo = UseInst;
+      }
+    }
+
+    const auto BBE = MBB->instr_end();
+    MachineBasicBlock::iterator DefI = BBE;
+    MachineBasicBlock::iterator UseI = BBE;
+
+    for (auto BBI = MBB->instr_begin(); BBI != BBE; ++BBI) {
+
+      if (DefI != BBE && UseI != BBE)
+        break;
+
+      if ((&*BBI != Def) && (&*BBI != UseToBringDefCloserTo))
+        continue;
+
+      if (&*BBI == Def) {
+        DefI = BBI;
+        continue;
+      }
+
+      if (&*BBI == UseToBringDefCloserTo) {
+        UseI = BBI;
+        continue;
+      }
+    }
+
+    if (DefI == BBE || UseI == BBE)
+      continue;
+
+    DEBUG({
+      dbgs() << "Splicing ";
+      DefI->dump();
+      dbgs() << " right before: ";
+      UseI->dump();
+    });
+
+    Changed = true;
+    MBB->splice(UseI, MBB, DefI);
+  }
+
+  return Changed;
+}
+
+/// Here we find our candidates. What makes an interesting candidate?
+/// An candidate for a canonicalization tree root is normally any kind of
+/// instruction that causes side effects such as a store to memory or a copy to
+/// a physical register or a return instruction. We use these as an expression
+/// tree root that we walk inorder to build a canonical walk which should result
+/// in canoncal vreg renaming.
+static std::vector<MachineInstr *> populateCandidates(MachineBasicBlock *MBB) {
+  std::vector<MachineInstr *> Candidates;
+  MachineRegisterInfo &MRI = MBB->getParent()->getRegInfo();
+
+  for (auto II = MBB->begin(), IE = MBB->end(); II != IE; ++II) {
+    MachineInstr *MI = &*II;
+
+    bool DoesMISideEffect = false;
+
+    if (MI->getNumOperands() > 0 && MI->getOperand(0).isReg()) {
+      const unsigned Dst = MI->getOperand(0).getReg();
+      DoesMISideEffect |= !TargetRegisterInfo::isVirtualRegister(Dst);
+
+      for (auto UI = MRI.use_begin(Dst); UI != MRI.use_end(); ++UI) {
+        if (DoesMISideEffect) break;
+        DoesMISideEffect |= (UI->getParent()->getParent() != MI->getParent());
+      }
+    }
+
+    if (!MI->mayStore() && !MI->isBranch() && !DoesMISideEffect)
+      continue;
+
+    DEBUG(dbgs() << "Found Candidate:  "; MI->dump(););
+    Candidates.push_back(MI);
+  }
+
+  return Candidates;
+}
+
+void doCandidateWalk(std::vector<TypedVReg> &VRegs,
+                     std::queue <TypedVReg> &RegQueue,
+                     std::vector<MachineInstr *> &VisitedMIs,
+                     const MachineBasicBlock *MBB) {
+
+  const MachineFunction &MF = *MBB->getParent();
+  const MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  while (!RegQueue.empty()) {
+
+    auto TReg = RegQueue.front();
+    RegQueue.pop();
+
+    if (TReg.isFrameIndex()) {
+      DEBUG(dbgs() << "Popping frame index.\n";);
+      VRegs.push_back(TypedVReg(RSE_FrameIndex));
+      continue;
+    }
+
+    assert(TReg.isReg() && "Expected vreg or physreg.");
+    unsigned Reg = TReg.getReg();
+
+    if (TargetRegisterInfo::isVirtualRegister(Reg)) {
+      DEBUG({
+        dbgs() << "Popping vreg ";
+        MRI.def_begin(Reg)->dump();
+        dbgs() << "\n";
+      });
+
+      if (!llvm::any_of(VRegs, [&](const TypedVReg &TR) {
+            return TR.isReg() && TR.getReg() == Reg;
+          })) {
+        VRegs.push_back(TypedVReg(Reg));
+      }
+    } else {
+      DEBUG(dbgs() << "Popping physreg.\n";);
+      VRegs.push_back(TypedVReg(Reg));
+      continue;
+    }
+
+    for (auto RI = MRI.def_begin(Reg), RE = MRI.def_end(); RI != RE; ++RI) {
+      MachineInstr *Def = RI->getParent();
+
+      if (Def->getParent() != MBB)
+        continue;
+
+      if (llvm::any_of(VisitedMIs,
+                       [&](const MachineInstr *VMI) { return Def == VMI; })) {
+        break;
+      }
+
+      DEBUG({
+        dbgs() << "\n========================\n";
+        dbgs() << "Visited MI: ";
+        Def->dump();
+        dbgs() << "BB Name: " << Def->getParent()->getName() << "\n";
+        dbgs() << "\n========================\n";
+      });
+      VisitedMIs.push_back(Def);
+      for (unsigned I = 1, E = Def->getNumOperands(); I != E; ++I) {
+
+        MachineOperand &MO = Def->getOperand(I);
+        if (MO.isFI()) {
+          DEBUG(dbgs() << "Pushing frame index.\n";);
+          RegQueue.push(TypedVReg(RSE_FrameIndex));
+        }
+
+        if (!MO.isReg())
+          continue;
+        RegQueue.push(TypedVReg(MO.getReg()));
+      }
+    }
+  }
+}
+
+// TODO: Work to remove this in the future. One day when we have named vregs
+// we should be able to form the canonical name based on some characteristic
+// we see in that point of the expression tree (like if we were to name based
+// on some sort of value numbering scheme).
+static void SkipVRegs(unsigned &VRegGapIndex, MachineRegisterInfo &MRI,
+                      const TargetRegisterClass *RC) {
+  const unsigned VR_GAP = (++VRegGapIndex * 1000);
+
+  DEBUG({
+    dbgs() << "Adjusting per-BB VR_GAP for BB" << VRegGapIndex << " to "
+           << VR_GAP << "\n";
+  });
+
+  unsigned I = MRI.createVirtualRegister(RC);
+  const unsigned E = (((I + VR_GAP) / VR_GAP) + 1) * VR_GAP;
+  while (I != E) {
+    I = MRI.createVirtualRegister(RC);
+  }
+}
+
+static std::map<unsigned, unsigned>
+GetVRegRenameMap(const std::vector<TypedVReg> &VRegs,
+                 const std::vector<unsigned> &renamedInOtherBB,
+                 MachineRegisterInfo &MRI,
+                 const TargetRegisterClass *RC) {
+  std::map<unsigned, unsigned> VRegRenameMap;
+  unsigned LastRenameReg = MRI.createVirtualRegister(RC);
+  bool FirstCandidate = true;
+
+  for (auto &vreg : VRegs) {
+    if (vreg.isFrameIndex()) {
+      // We skip one vreg for any frame index because there is a good chance
+      // (especially when comparing SelectionDAG to GlobalISel generated MIR)
+      // that in the other file we are just getting an incoming vreg that comes
+      // from a copy from a frame index. So it's safe to skip by one.
+      LastRenameReg = MRI.createVirtualRegister(RC);
+      DEBUG(dbgs() << "Skipping rename for FI " << LastRenameReg << "\n";);
+      continue;
+    } else if (vreg.isCandidate()) {
+
+      // After the first candidate, for every subsequent candidate, we skip mod
+      // 10 registers so that the candidates are more likely to start at the
+      // same vreg number making it more likely that the canonical walk from the
+      // candidate insruction. We don't need to skip from the first candidate of
+      // the BasicBlock because we already skip ahead several vregs for each BB.
+      while (LastRenameReg % 10) {
+        if (!FirstCandidate) break;
+        LastRenameReg = MRI.createVirtualRegister(RC);
+
+        DEBUG({
+          dbgs() << "Skipping rename for new candidate " << LastRenameReg
+                 << "\n";
+        });
+      }
+      FirstCandidate = false;
+      continue;
+    } else if (!TargetRegisterInfo::isVirtualRegister(vreg.getReg())) {
+      LastRenameReg = MRI.createVirtualRegister(RC);
+      DEBUG({
+        dbgs() << "Skipping rename for Phys Reg " << LastRenameReg << "\n";
+      });
+      continue;
+    }
+
+    auto Reg = vreg.getReg();
+    if (llvm::find(renamedInOtherBB, Reg) != renamedInOtherBB.end()) {
+      DEBUG(dbgs() << "Vreg " << Reg << " already renamed in other BB.\n";);
+      continue;
+    }
+
+    auto Rename = MRI.createVirtualRegister(MRI.getRegClass(Reg));
+    LastRenameReg = Rename;
+
+    if (VRegRenameMap.find(Reg) == VRegRenameMap.end()) {
+      DEBUG(dbgs() << "Mapping vreg ";);
+      if (MRI.reg_begin(Reg) != MRI.reg_end()) {
+        DEBUG(auto foo = &*MRI.reg_begin(Reg); foo->dump(););
+      } else {
+        DEBUG(dbgs() << Reg;);
+      }
+      DEBUG(dbgs() << " to ";);
+      if (MRI.reg_begin(Rename) != MRI.reg_end()) {
+        DEBUG(auto foo = &*MRI.reg_begin(Rename); foo->dump(););
+      } else {
+        DEBUG(dbgs() << Rename;);
+      }
+      DEBUG(dbgs() << "\n";);
+
+      VRegRenameMap.insert(std::pair<unsigned, unsigned>(Reg, Rename));
+    }
+  }
+
+  return VRegRenameMap;
+}
+
+static bool doVRegRenaming(std::vector<unsigned> &RenamedInOtherBB,
+                           const std::map<unsigned, unsigned> &VRegRenameMap,
+                           MachineRegisterInfo &MRI) {
+  bool Changed = false;
+  for (auto I = VRegRenameMap.begin(), E = VRegRenameMap.end(); I != E; ++I) {
+
+    auto VReg = I->first;
+    auto Rename = I->second;
+
+    RenamedInOtherBB.push_back(Rename);
+
+    std::vector<MachineOperand *> RenameMOs;
+    for (auto &MO : MRI.reg_operands(VReg)) {
+      RenameMOs.push_back(&MO);
+    }
+
+    for (auto *MO : RenameMOs) {
+      Changed = true;
+      MO->setReg(Rename);
+
+      if (!MO->isDef())
+        MO->setIsKill(false);
+    }
+  }
+
+  return Changed;
+}
+
+static bool doDefKillClear(MachineBasicBlock *MBB) {
+  bool Changed = false;
+
+  for (auto &MI : *MBB) {
+    for (auto &MO : MI.operands()) {
+      if (!MO.isReg())
+        continue;
+      if (!MO.isDef() && MO.isKill()) {
+        Changed = true;
+        MO.setIsKill(false);
+      }
+
+      if (MO.isDef() && MO.isDead()) {
+        Changed = true;
+        MO.setIsDead(false);
+      }
+    }
+  }
+
+  return Changed;
+}
+
+static bool runOnBasicBlock(MachineBasicBlock *MBB,
+                            std::vector<StringRef> &bbNames,
+                            std::vector<unsigned> &renamedInOtherBB,
+                            unsigned &basicBlockNum, unsigned &VRegGapIndex) {
+
+  if (CanonicalizeBasicBlockNumber != ~0U) {
+    if (CanonicalizeBasicBlockNumber != basicBlockNum++)
+      return false;
+    DEBUG(dbgs() << "\n Canonicalizing BasicBlock " << MBB->getName() << "\n";);
+  }
+
+  if (llvm::find(bbNames, MBB->getName()) != bbNames.end()) {
+    DEBUG({
+      dbgs() << "Found potentially duplicate BasicBlocks: " << MBB->getName()
+             << "\n";
+    });
+    return false;
+  }
+
+  DEBUG({
+    dbgs() << "\n\n  NEW BASIC BLOCK: " << MBB->getName() << "  \n\n";
+    dbgs() << "\n\n================================================\n\n";
+  });
+
+  bool Changed = false;
+  MachineFunction &MF = *MBB->getParent();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  const unsigned DummyVReg = GetDummyVReg(MF);
+  const TargetRegisterClass *DummyRC =
+    (DummyVReg == ~0U) ? nullptr : MRI.getRegClass(DummyVReg);
+  if (!DummyRC) return false;
+
+  bbNames.push_back(MBB->getName());
+  DEBUG(dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << "\n\n";);
+
+  DEBUG(dbgs() << "MBB Before Scheduling:\n"; MBB->dump(););
+  Changed |= rescheduleCanonically(MBB);
+  DEBUG(dbgs() << "MBB After Scheduling:\n"; MBB->dump(););
+
+  std::vector<MachineInstr *> Candidates = populateCandidates(MBB);
+  std::vector<MachineInstr *> VisitedMIs;
+  std::copy(Candidates.begin(), Candidates.end(),
+            std::back_inserter(VisitedMIs));
+
+  std::vector<TypedVReg> VRegs;
+  for (auto candidate : Candidates) {
+    VRegs.push_back(TypedVReg(RSE_NewCandidate));
+
+    std::queue<TypedVReg> RegQueue;
+
+    // Here we walk the vreg operands of a non-root node along our walk.
+    // The root nodes are the original candidates (stores normally).
+    // These are normally not the root nodes (except for the case of copies to
+    // physical registers).
+    for (unsigned i = 1; i < candidate->getNumOperands(); i++) {
+      if (candidate->mayStore() || candidate->isBranch())
+        break;
+
+      MachineOperand &MO = candidate->getOperand(i);
+      if (!(MO.isReg() && TargetRegisterInfo::isVirtualRegister(MO.getReg())))
+        continue;
+
+      DEBUG(dbgs() << "Enqueue register"; MO.dump(); dbgs() << "\n";);
+      RegQueue.push(TypedVReg(MO.getReg()));
+    }
+
+    // Here we walk the root candidates. We start from the 0th operand because
+    // the root is normally a store to a vreg.
+    for (unsigned i = 0; i < candidate->getNumOperands(); i++) {
+
+      if (!candidate->mayStore() && !candidate->isBranch())
+        break;
+
+      MachineOperand &MO = candidate->getOperand(i);
+
+      // TODO: Do we want to only add vregs here?
+      if (!MO.isReg() && !MO.isFI())
+        continue;
+
+      DEBUG(dbgs() << "Enqueue Reg/FI"; MO.dump(); dbgs() << "\n";);
+
+      RegQueue.push(MO.isReg() ? TypedVReg(MO.getReg()) :
+                                  TypedVReg(RSE_FrameIndex));
+    }
+
+    doCandidateWalk(VRegs, RegQueue, VisitedMIs, MBB);
+  }
+
+  // If we have populated no vregs to rename then bail.
+  // The rest of this function does the vreg remaping.
+  if (VRegs.size() == 0)
+    return Changed;
+
+  // Skip some vregs, so we can recon where we'll land next.
+  SkipVRegs(VRegGapIndex, MRI, DummyRC);
+
+  auto VRegRenameMap = GetVRegRenameMap(VRegs, renamedInOtherBB, MRI, DummyRC);
+  Changed |= doVRegRenaming(renamedInOtherBB, VRegRenameMap, MRI);
+  Changed |= doDefKillClear(MBB);
+
+  DEBUG(dbgs() << "Updated MachineBasicBlock:\n"; MBB->dump(); dbgs() << "\n";);
+  DEBUG(dbgs() << "\n\n================================================\n\n");
+  return Changed;
+}
+
+bool MIRCanonicalizer::runOnMachineFunction(MachineFunction &MF) {
+
+  static unsigned functionNum = 0;
+  if (CanonicalizeFunctionNumber != ~0U) {
+    if (CanonicalizeFunctionNumber != functionNum++)
+      return false;
+    DEBUG(dbgs() << "\n Canonicalizing Function " << MF.getName() << "\n";);
+  }
+
+  // we need a valid vreg to create a vreg type for skipping all those
+  // stray vreg numbers so reach alignment/canonical vreg values.
+  std::vector<MachineBasicBlock*> RPOList = GetRPOList(MF);
+
+  DEBUG(
+    dbgs() << "\n\n  NEW MACHINE FUNCTION: " << MF.getName() << "  \n\n";
+    dbgs() << "\n\n================================================\n\n";
+    dbgs() << "Total Basic Blocks: " << RPOList.size() << "\n";
+    for (auto MBB : RPOList) {
+      dbgs() << MBB->getName() << "\n";
+    }
+    dbgs() << "\n\n================================================\n\n";
+  );
+
+  std::vector<StringRef> BBNames;
+  std::vector<unsigned> RenamedInOtherBB;
+
+  unsigned GapIdx = 0;
+  unsigned BBNum = 0;
+
+  bool Changed = false;
+
+  for (auto MBB : RPOList)
+    Changed |= runOnBasicBlock(MBB, BBNames, RenamedInOtherBB, BBNum, GapIdx);
+
+  return Changed;
+}
+